Billionaire Donald Trump is leading the Republican field in the latest national poll from The Economist/YouGov.

Trump is four points ahead of former Florida Gov. Jeb Bush and Kentucky Sen. Rand Paul, who are tied for second place, in the poll taken July 4-6 of 1,000 registered voters.

Donald Trump: 15 percent

Jeb Bush: 11 percent

Rand Paul: 11 percent

Scott Walker: 9 percent

Marco Rubio: 9 percent

Mike Huckabee: 9 percent

Ben Carson: 7 percent

Chris Christie: 6 percent

Ted Cruz: 4 percent

Carly Fiorina: 3 percent

Rick Perry: 2 percent

Rick Santorum: 2 percent

John Kasich: 2 percent

Lindsey Graham: 1 percent

George Pataki: 0 percent

In addition, 12 percent of registered voters said that Trump is their second-choice pick. When the two numbers are combined, that means one-in-four Republican voters see the real estate mogul as either their first or second choice.

Two-thirds of those who said Trump was either their first or second choice also said that they are tea party supporters, and several of his supporters identified as "very conservative," which means that Trump's recent comments on immigration may be hitting a nerve.

Trump's favorable rating has also increased in recent weeks. In mid-June, 38 percent of Republicans had a favorable view of the reality TV star. That number has since jumped 11 percentage points, with 49 percent of GOP voters now saying they view him favorably.

However, Republicans don't think Trump will actually win the nomination.

Only 7 percent of registered Republican voters think Trump will be the GOP's presidential nominee in 2016. Twenty-nine percent said it will be Bush, 12 percent expect Paul to win the nomination, and Rubio and Walker are tied with 8 percentage points.

Trump is also leading the GOP field in North Carolina, according a new poll by the Public Policy Polling group.